In conventional semiconductor technology, optical measurement techniques may be used to monitor and test structural parameters of semiconductor devices in semiconductor manufacturing, such as a feature size of a semiconductor device. Specifically, in semiconductor manufacturing, when a semiconductor device is being formed on a substrate, a corresponding structure for optical measurement may be formed in a cutting area. As shown in FIG. 1, a structure for optical measurement 1 includes a plurality of repeating units along a direction A, e.g., a straight line. The structure for optical measurement 1 is made of the same material(s) as the corresponding semiconductor device and is formed through the same steps. The structure for optical measurement 1 has identical structural parameters as the corresponding semiconductor device. Therefore, structural parameters of the structure for optical measurement 1 may be used to represent structural parameters of the corresponding semiconductor structure. By measuring structural parameters of the structure for optical measurement, the structural parameters of the corresponding semiconductor device may be obtained.
Specifically, the conventional method of optical measurements includes several steps. First of all, as shown in FIG. 1, light spot 2 may be used to illuminate the structure for optical measurement 1 such that light scatters in the structure for optical measurement 1. Optical detectors receive the incident light and scattered light for analysis and modulation. A measured scattering spectrum may be obtained.
Further, the obtained measured light scattering spectrum may be matched with each standard optical scattering spectrum in a library or database. If a match is obtained between the obtained light scattering spectrum and a standard optical scattering spectrum, the structural parameters of the standard semiconductor device structure corresponding to the standard optical scattering spectrum is considered as the structural parameters of the structure for optical measurement 1. The parameters of the standard semiconductor device structure corresponding to the standard optical scattering spectrum is further used as the structural parameters of the semiconductor device structure corresponding to the structure for optical measurement 1 and is used to estimate the quality of the semiconductor device structure. If no matching standard optical scattering spectrum may be found for the obtained light scattering spectrum, the structural parameters of the semiconductor device structure formed are considered as failing to meet the predetermined standards, and the semiconductor device structures are not qualified as good products.
However, in the conventional technology, as shown in FIG. 2, the light spot 2′ often deviates from the area of the structure for optical measurement 1′ and illuminates on a plain or void area on the substrate. Light reflection from the plain area may generate noise and reduce the reliability of the obtained light scattering spectrum. That is, the measured structure, reflected by the structural parameters, based on the obtained light scattering spectrum may not be accurate, and the obtained structural parameters of the semiconductor device structure may not be accurate.
Several solutions were developed to solve the problem mentioned above. For example, one solution includes increasing or expanding the size of the cutting area containing the structure for optical measurement. However, due to limited scribe-line space, such solution may be difficult to implement. Another solution includes decreasing or shrinking the size of the illuminating light spot to lower the probability of the light spot deviating from the structure for optical measurement so that the signal-to-noise ratio may be decreased. However, such solution often requires modifications to the corresponding equipment and thus the manufacturing cost may increase.
The disclosed methods and systems are directed to solve one or more problems set forth above and other problems.